Add the metalava_enabled property

The new property is added for supporting metalava. But some sdk library
cannot use metalava. So "metalava_enabled: false" is added to these
modules.

Test: make -j
Test: checkapi
Bug: 117127012
Change-Id: Ib65f3cd73dac0ac6ed64afeca6546d99739e4424
diff --git a/media/lib/signer/Android.bp b/media/lib/signer/Android.bp
index 3b25787..8c43683 100644
--- a/media/lib/signer/Android.bp
+++ b/media/lib/signer/Android.bp
@@ -18,4 +18,5 @@
     name: "com.android.mediadrm.signer",
     srcs: ["java/**/*.java"],
     api_packages: ["com.android.mediadrm.signer"],
+    metalava_enabled: false,
 }